Simulation study on 3H behavior in the Fukushima coastal region: Comparison of influences of discharges from the Fukushima Daiichi and rivers.

The release of tritium (3H) to the ocean is planned on the coastal environment in the Fukushima coastal region from Spring or Summer of 2023. Before its release, we evaluate the effect of 3H discharges from the port of Fukushima Daiichi and rivers in the Fukushima coastal region using a three-dimensional hydrodynamic model (3D-Sea-SPEC). The simulation results showed that discharges from the port of Fukushima Daiichi dominantly affected the 3H concentrations in monitoring points within approximately 1 km. Moreover, the results indicate that the effect of riverine 3H discharge was limited around the river mouth under base flow conditions. However, its impact on the Fukushima coastal regions under storm flow conditions was found, and the 3H concentrations in seawater in the Fukushima coastal region were formed around 0.1 Bq/L (mean 3H concentrations in seawater in the Fukushima coastal region) in the near shore.